this ppt is all about flash memory.

1. PROGRAMMABLE ARRAY
LOGIC

2. Programmable Logic
Devices

3.  PLDs
 Programmable Logic Devices (PLD)
 General purpose chip for implementing circuits
 Can be customized using programmable switches
 Main types of PLDs
 PLA
 PAL
 ROM
 CPLD
 FPGA
 Custom chips: standard cells, sea of gates

4.  PLD as a Black Box
Logic gates
and
programmable
switches
Inputs
(logic variables)
Outputs
(logic functions)

5. Basic Programmable Logic
Organizations
 Depending on which of the AND/OR logic
arrays is programmable, we have three
basic organizations
AND ARRAY
PROG.
FIXED
PROG.
OR ARRAY
FIXED
PROG.
PROG.
ORGANIZATION
PAL
PROM
PLA

6. Programmable Array Logic
 EARLY HISTORY:-
 Before PALs were introduced, designers of digital logic circuits would use small-scale
integration (SSI) components, such as those in the 7400 series TTL
(transistor-transistor logic) family; the 7400 family included a variety of logic building
blocks, such as gates (NOT, NAND, NOR, AND, OR), multiplexers (MUXes) and
demultiplexers (DEMUXes), flip flops (D-type, JK, etc.) and others. One PAL device
would typically replace dozens of such "discrete" logic packages, so the SSI
business went into decline as the PAL business took off. PALs were used
advantageously in many products, such as minicomputers, as documented in Tracy
Kidder's best-selling book "The Soul of a New Machine."
 PALs were not the first commercial programmable logic devices; Signetics had been
selling its field programmable logic array (FPLA) since 1975. These devices were
completely unfamiliar to most circuit designers and were perceived to be too difficult
to use. The FPLA had a relatively slow maximum operating speed (due to having
both programmable-AND and programmable-OR arrays), was expensive, and had a
poor reputation for testability. Another factor limiting the acceptance of the FPLA
was the large package, a 600-mil (0.6", or 15.24 mm) wide 28-pin dual in-line
package (DIP).

7. PALs
 The project to create the PAL device was managed by John Birkner and the
actual PAL circuit was designed by H. T. Chua.[3] In a previous job, Birkner
had developed a 16-bit processor using 80 standard logic devices. His
experience with standard logic led him to believe that user programmable
devices would be more attractive to users if the devices were designed to
replace standard logic. This meant that the package sizes had to be more
typical of the existing devices, and the speeds had to be improved. The
PAL met these requirements and was a huge success and was "second
sourced" by National Semiconductor, Texas Instruments, and Advanced
Micro Devices.
 Early PALs were 20-pin DIP components fabricated in silicon using bipolar
transistor technology with one-time programmable (OTP) titanium-tungsten
programming fuses.[4] Later devices were manufactured by Lattice
Semiconductor and Advanced Micro Devices using CMOS technology.
 The original 20 and 24-pin PALs were denoted by MMI as medium-scale
integration (MSI) devices.

8. PAL ARCHITECTURE

9. PALs
 The programmable elements (shown as a fuse) connect both the true and
complemented inputs to the AND gates. These AND gates, also known as
product terms, are ORed together to form a sum-of-products logic array.
 The PAL architecture consists of two main components: a logic plane and
output logic macrocells.
 Programmable logic plane
 The programmable logic plane is a programmable read-only memory
(PROM) array that allows the signals present on the devices pins (or the
logical complements of those signals) to be routed to an output logic
macrocell.
 PAL devices have arrays of transistor cells arranged in a "fixed-OR,
programmable-AND" plane used to implement "sum-of-products" binary
logic equations for each of the outputs in terms of the inputs and either
synchronous or asynchronous feedback from the outputs.

10.  Programmable Array Logic (PAL)
 Also used to implement
circuits in SOP form
 The connections in
the AND plane are
programmable
 The connections in
the OR plane are
NOT programmable
and
AND plane OR plane
f 1
Input buffers
inverters
P 1
P k
f m
x 1 x 2 x n
x 1 x 1 x n x n
fixed connections

11.  Example Schematic of a PAL
f 1
P 1
P 2
f 2
x 1 x 2 x 3
AND plane
P 3
P 4
f1 = x1x2x3'+x1'x2x3
f2 = x1'x2'+x1x2x3

12. PALs and PLAs
What is difference between Programmable Array Logic (PAL) and
Programmable Logic Array (PLA)?
PAL concept — implemented by Monolithic Memories
AND array is programmable, OR array is fixed at fabrication
A given column of the OR array
has access to only a subset of
the possible product terms
PLA concept — Both AND and OR arrays are programmable

13. PALs and PLAs
 Of the two organizations the PLA is the most
flexible
 One PLA can implement a huge range of logic
functions
 BUT many pins; large package, higher cost
 PALs are more restricted / you trade number of
OR terms vs number of outputs
 Many device variations needed
 Each device is cheaper than a PLA

14. PAL
1st output
section
2nd output
section
3rd output
section
4th output
section
Only functions
with
at most four
products can be
implemented
inputs

15. PAL
x
x
W = ABC + CD
X = ABC + ACD + ACD + BCD
Y = ACD + ACD + ABD
x

16. PAL Logic Implementation
Programmed PAL:
Minimized Functions:
W = A + B D + B C
X = B C
Y = B + C
Z = A B C D + B C D + A D + B C D
4 product terms per each OR gate
A B C D
A B C D
A
BD
BC
0
0
0
0
B
C
0
0
BC
BCD
AD
BCD
W X Y Z

17. THANK
YOU
THANKS